Increased turbine engine performance has been achieved through the improvements to turbine alloys, cooling scheme, and coatings. The most improvement from coatings has been through the addition of thermal barrier coatings (TBC) to cooled turbine components. For turbine blades, the most effective TBC has been applied by Electron Beam Physical Vapor Deposition (PVD). Prior art includes NiCoCrAlY, aluminide and platinum-aluminide bond coats. Evolutionary improvements to these bond coats has been realized in terms of optimal processing to produce improved surface finish or clean processing to reduce the significant effect of contaminates such as S (sulfur). However, turbine designers are not making full use of TBCs because their predicted life does not meet the component design life at higher turbine temperature or TBC life at existing temperatures are not reliable. Consequently a need for more reliable and longer life TBCs exists.
Addition of Hf to alloys is relatively easy and has shown a significant impact on TBC spallation life when high Hf alloys [higher than single crystal alloys (SXL) specification or directional solidification (DS) alloys with high Hf for improved castability] are coated with current outward type Pt—Al aluminide bond coats. SXL alloys have shown 3× to 5× (3 times to 5 times) life improvement while DS MarM247 has been reported to have 10× life improvement relative to baseline SXL TBC life. For SXL, the high Hf additions impacted SXL alloy microstructure and mechanical properties negatively.